Flexible plasticized explosive of cyclonitramine and nitrocellose and process therefor



United States Patent FLEXIBLE PLASTICIZED EXPLOSIVE 0F CYCLO- NITRAMINE AND NITROCELLOSE AND PROC- ESS THEREFOR John D. Hopper, Succasunna, and Franklin B. Wells, Jefferson Township, Morris County, N.J., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Filed Oct. 27, 1965, Ser. No. 505,445

13 Claims. (Cl. 149-18) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to an explosive composition and more particularly concerns a flexible, self-supporting, Water-resistant explosive and a method for its prepara tion.

Our composition comprises a particulate explosive and a plasticized binder, the composition being useful in explosive metal-forming processes and admirably well suited for demolition purposes. The composition is characterized further by safety in handling, and it may be formed readily into any desired shape as by rolling, extrusion, compression-molding, etc., into strips, blocks, sheets, and the like.

It is therefore an object of this invention to provide an explosive having the aforementioned characteristics.

Another object of this invention is to provide a flexible explosive of high power (at least the equivalent of TNT) and brisance (rate of detonation about 7000 m./sec.).

Still another object of this invention is to provide an explosive which, in sheet form, possesses suflicient flexibility so that it may be made to conform to the contour of uneven surfaces with a minimum of manipulation, thus aiding in the complete destruction of the device to be demolished.

A further object of this invention is to provide a flexible explosive having high resistance to impact and friction While retaining good cap sensitivity characteristics.

A still further object of this invention is to provide a flexible explosive which is more heat-stable than similar materials currently available.

Yet another object of this invention is to provide a flexible explosive which is not adversely affected by Water.

A final object of this invention is to provide an explosive of sufficient resiliency so that, when made in block or other massive form, it will resist breaking up upon impact with a hard surface when striking such a surface with a velocity of at least 150 feet/second.

Other and further objects of this invention will become apparent as the invention is further described hereinafter.

We have found that the foregoing objects may be attained through provision of an explosive composition comprising about 4576% cyclotrimethylenetrinitramine, hereinafter referred to as RDX, and or cyclotetramethylenetetranitramine, hereinafter referred to as HMX, the said RDX and/ or HMX having an average particle size of up to about 25 microns, preferably not over 13 microns. One hundred percent of the RDX and/or HMX must pass through a #200 US. Standard sieve, and at least 90%, and preferably not less than 97.5%, should pass through a #325 US. Standard sieve.

Our composition will also contain about 17-39%, preferably about 25-30% of a plasticizer such as tributyl acetylcitrate (preferred), dioctyl sebacate, triethylene glycol di(2-ethylbutyrate), or other similar materials, preferably those having pour points of 40 C. or below, about 545%, preferably about 68%, of nitrocellulose containing about 12.112.5% nitrogen, of such a degree of polymerization as to have a viscosity, using a 4% solution of nitrocellulose and a 7 inch diameter steel ball,

of at least seconds and preferably greater than 140 seconds, and about 0.0-1.0%, preferably about 0.30.8%, of a pigment to impart any desired color to the finished product.

In the determination of viscosity aforementioned, the steel ball shall weigh about 2.025 to 2.045 grams and the viscosimeter shall consist of a glass tube 14 inches in length with an internal diameter of 1 inch, being immersed up to the level of its liquid contents in a constant temperature bath maintained at 25i0.2 C. and the time of passage of the balls between markings noted.

The aforementioned viscosity test is run in accordance with Specification MILN244A, paragraph 4.4.5 et seq., dated Feb. 13, 1962, With the exception that the quantities of materials used are: 8 grams nitrocellulose, 21.3 grams of ethyl alcohol, and 170.7 grams of acetone. The 21.3-gram/ 170.7-gram alcohol/ acetone ratio is used to maintain the ratio required in the specification.

While varying the proportions of all three of the major ingredients of our explosive results in some variations in the properties thereof, We have found in a series of fifteen tests that, in general, the presence of less than 45% RDX and/ or HMX gives a product having reduced self-supporting properties and reduced power; whereas a content of more than 76% RDX and/or HMX results in reduced cohesive power. A content of less than 17% plasticizer results in reduced strength and cohesiveness; Whereas the presence of more than 39% plasticizer results in a sticky product having reduced self-supporting properties. Less than 5% nitrocellulose in the product results in reduced strength; whereas the presence of more than 15% nitrocellulose results in a product that is not sufliciently moldable. We have found, also, that substitution of even a minor proportion of the specified nitrocellulose by ordinary low-viscosity nitrocellulose results in a sticky prodnot with reduced self-supporting properties.

For purposes of camouflage, an olive-drab coloration of the explosive is most desirable. Less than 0.2% pig- 1 meat is insufficient to give a satisfactory coloration to the product where a color other than White is desired, and the presence of more than 1% pigment is not necessary for effective coloring. The preferred pigment, which imparts an olive-drab coloration to our explosive, comprises one part lampblack and 8 parts chrome yellow, medium (lead chromate).

The presence of about 0.4% (5% based on nitrocellulose present) diphenylamine, referred to hereinafter as DPA, improved the heat stability of our product to such an extent that the gas evolved in the 40-hour 110 C. Vacuum Stability Test with a S-gram sample was reduced by about 50%. Quantities other than 0.4% DPA all resulted in a reduced stabilizing effect. The Vacuum Stability Test is described in specification Standard MIL-STD-650, Method 503.1 at C.

Our product employing RDX and/or HMX as the high explosive base provides unexpected and unpredictable advantages over flexible explosives containing PE'IN as the high explosive base.

Compositions containing RDX and/or HMX showed substantially greater thermal stability in the vacuum stability test than did those containing PETN. According to Picatinny Arsenal Technical Report No. 1740, Revision 1, April 1958, the vacuum stability values of PETN, RDX, and HMX at 100 C. are 0.5 ml., 0.7 ml., and 0.35 ml., respectively. It would be expected, therefore, that flexible explosive compositions differing only in that they are based on these three explosive materials should have almost identical thermal stabilities, but this has not been found to be the case. A series of vacuum stability tests, not included in the examples, showed that in the 40-hour 100 C. Vacuum Stability Test, using S-gram samples, the PETN-based flexible explosive composition yielded about 1.5 ml. of gas while similar RDX- and/or HMX-based flexible explosive compositions yielded about 0.75 ml. of gas. The advantage in the use of RDX and/or HMX becomes much more striking in the same test at 110 C. where unstabilized RDX- and/ or HMX-based flexible explosive compositions yielded 4-5 ml. of gas, and various batches of a similar PETN-based composition yielded 11+ ml., usually in much less than 40 hours. The capacity of the apparatus used is 11 ml. The improved vacuum stability found for the RDX- and/ or HMX-based flexible explosive compositions, therefore, is not predictable on the basis of the cited vacuum stability values for PETN, RDX, and HMX. Further examples of the improved thermal stability obtained through the use of RDX and/ or HMX are found in Examples I, II, III, and V.

To further reveal the superiority of our product over a commercial PETN containing flexible explosive, samples thereof were tested in a circulating hot-air oven at 160:5 F. Some of the samples of the PETN-based explosive developed wrinkles and puckers in 2-3 days which grew to patches of 1 inch or more in maximum dimension until the 7th or 8th day of the test after which they remained static. None of our RDX-containing samples developed any such imperfections during a test period of 6 weeks. This test further illustrates an unpredictable advantage of our RDX-containing flexible explosive.

Again, in exudation properties, our flexible explosive proved superior to the PETN 'based flexible explosive. The exudation test at 160 F. is carried out as follows: The explosive sheet shall be inch thick and cut to 1% inch square and then placed on layers of filter paper out in 2-inch diameter circles. A porous release paper shall be placed between the flexible explosive and the layers of filter paper. A 125-gram brass weight, 1% inch square, shall be placed on top of the sample. This assembled sample shall then be placed on a wire screen and stored in a forced draft oven for 24 hours at 160 F. Before assembly, the brass weight shall be weighed, and then reweighed with the sample. After hot storage, the sample and brass weight shall be removed from the filter paper while still warm, no attempt being made to separate the brass weight from the sample, and allowed to cool upside down. When cool, the sample and brass weight shall be weighed together. The test shall be run in triplicate and the average of three results shall be reported to determine compliance with the requirement.

Our material readily met the requirement of the above exudation test, which provides for an allowable limit of 0.1%, by yielding values ranging between 0.090 to 0.094%, whereas the PETN-based flexible explosive failed by yielding results ranging between 0.11 to 0.20%.

In cap sensitivity tests it was found that the commercial PETN-containing flexible explosive showed wide variations in sensitivity to initiation, not only from lot to lot also within a given lot. This is exemplified by two extremes of one lot which both accepted and failed to accept initiation from standard #3, #4, #5, and #6 caps while accepting initiation consistently from standard #8 caps, and another lot which both accepted and failed to accept initiation from standard #1 caps while accepting initiation consistent-1y from standard #2 caps. Our RDX- containing material, on the other hand, accepted initiation from standard #8 blasting caps, but failed to do so from standard #6 blasting caps. Our HMX-containing material accepted initiation from caps containing 13.5 grains of RDX, but failed to do so from standard #8 blasting caps. The erratic behavior of the PETN-containing material with respect to cap sensitivity constitutes an unexpected safety feature inherent in our RDX- and/ or HMX- containing flexible explosives. In caps, as is well known in the art, the smaller the number of the cap, the less explosive charge is contained therein.

fit

We have also devised a method for preparing our compositions which offers distinct advantages over conventional methods. An outstanding advantage to be derived from one of our methods is the granular form of the product which renders it particularly well suited for extrusion and compression-molding purposes.

In accordance with this method, nitrocellulose of the high viscosity type aforementioned containing about 12.1 to 12.5% nitrogen is dissolved in about 3070 parts solvent (preferably 4850 times its weight) such as butyl (preferred), propyl, or ethyl acetate with mechanical agitation. When solution of the nitrocellulose is complete, the stabilizer is added and dissolved and the plasticizer in amounts aforementioned is then stirred into the solution. The stabilizer will preferably be 0.4% DPA as aforementioned. The RDX and/or HMX is separately suspended in about 20-80 (preferably 58-60) times its weight of water held at C. in an open vessel. The RDX or HMX may be suspended without the presence of the other, or a mixture of both in any proportion would also be satisfactory. The nitrocellulose solution is added slowly in a fine stream to the vigorously agitated RDX and/ or HMX suspension so that it is well dispersed therein. When all of the nitrocellulose solution has been added, the temperature of the constantly stirred mixture is raised to -98 C. to distill off the solvent, which, preferably, is collected for reuse. The mixture is then cooled to 40 C. as rapidly as possible and filtered, after which the product, in the form of small somewhat irregular pellets, is air-dried until all apparent moisture has evaporated. It is then oven-dried to constant weight at 60 C. The granular product thus obtained is relatively free-flowing when first prepared. Upon standing, the granules tend to adhere lightly to one another, but the aggregate may be broken up readily, if desired. It may be processed in any desired manner as by extrusion, rolling, molding, etc.

The products and processes of our invention are further described and illustrated by the examples hereinunder set forth.

Example I Thirty-one and one-half grams of dry RDX containing about 7.3% HMX and 14.1 grams tributyl acetylcitrate plasticizer were mixed for three minutes in a sigma blade mixer held at 135:t5 F. to form a uniform pasty mass. Four grams of high-viscosity nitrocellulose containing about 12.1 to 12.5 nitrogen and 0.4 gram of the lampblack-chrome yellow pigment were then mixed in and enough ethyl alcohol added to change the consistency of the mix to that of thick dough. About 15 ml. of alcohol was used. The dough was mixed a total of 15 minutes at 135 i5 F. and then transferred to a roll mill, also at 135i5 F., where it was rolled at a roll gap setting of 0.010-inch until the odor of alcohol was no longer detectable. The roll gap was then increased to 0.210-inch and the material consolidated into a Ai-inch thick sheet which was smooth, apparently uniform, and had a vacuum stability value at C. of 4.94 ml. (evolved gas) at standard temperature and pressure.

*Dry basis.

The RDX and plasticizer were mixed 3 minutes at F. The mixer was then stopped and tilted to decant the water. The alcohol-wet nitrocellulose and the pigment were added and the whole mixed 30 minutes with the mixer held at 130 F. and the top open. The mix was then rolled as described in Example I to give uniform homogeneous sheets having a vacuum stability value of Rate of detonation (m./sec.) 7044.

Cap sensitivity test #8.

Friction pendulum test (steel No crackles, flame,

shoe) or explosion. Ballistic mortar test (TNT value) 1.0. Picatinny arsenal impact sensitivity test Rifle bullet impact test at 40 feet (3" x 3" x A sheet sandwiched between a 3" X 3" x A mild steel face plate and a 3" x 3" x 1" mild steel back-up plate) Elevated temperature test (160:5 F. for 6 weeks) 14 inches.

No fire or explosion.

No change in appearance or flexibility.

Hot water immersion test (160 F.

for 24 hours) No change in appearance or flexibility.

Exudation test (loss) 0.09%.

Bar drop test (10 lb. bar with /2- inch diameter and dropped 15 ft. endwise onto a 0.080-inch thick sample on a steel anvil) No fire or explosion.

Picatinny arsenal explosion temperature test 268 C. (decomp.).

The symbol 4, indicates the density of the material at 20 C. as compared to the density of water at 4 C.

The Friction Pendulum Test (steel shoe) and Ballistic Mortar Test are described by J. H. McIvor in Picatinny Arsenal Testing Manuals 7-1 and 7-2, respectively, both dated May 8, 1950.

The Picatinny Arsenal Impact Sensitivity Test and Explosion Temperature Test are described in Standard Laboratory Procedures for Sensitivity, Brisance, and Stability of Explosives, PATR No. 1401, March 18, 1944, Revised February 28, 1950, W. H. Rinkenbach and A. J. Clear.

The Rifle Bullet Impact Test and Elevated Temperature Test are described in Military Specification MIL-E- 46676A (MU), April 17, 1964, paragraphs 4.3.7 and 4.3.11, respectively, except that our samples were subjected to temperatures of 160 :5 F. for 6 weeks in lieu of the 7 days specified in the above specification. Similarly, in the specification (4667 6A), the Hot Water Immersion Test and Bar Drop Test may be found in paragraphs 4.3.15 and 4.3.9, respectively.

Example III The composition of this example was identical in formulation with that of Example II except that HMX containing about 1.2% RDX was used. A smooth homogeneous sheet was obtained having characteristics and physical properties similar to those of the product of Example II but the Vacuum Stability Test gave a value of 4.58 ml. at 110 C. and initiation required 13.5 grains of RDX. (This is a more powerful explosive charge than that ina #8 cap and a less powerful charge than that in a #10 cap.)

Example IV The composition of the flexible explosive of this example was identical in formulation with that of Example II except that RDX containing about 2.5% HMX was used. The characteristics of the resultant product were substantially identical with those of the product of Example II.

6 Example V The composition of this example was identical in formulation with that of Example II except that it contained 0.4 added part of DPA (based on parts of flexible explosive as prepared in Example II), which was dissolved in the alcohol contained in the nitrocellulose. This mixture gave a product very similar to that of Example II except that its Vacuum Stability Value at C. was 2.85 ml., a considerable improvement over the value found for the unstabilized material.

Example VI The composition of the flexible explosive prepared according to this example was identical with that of Example V, a new precipitation method of preparation being employed. In accordance with this method, 24 grams high viscosity nitrocellulose was dissolved in 1176 grams butyl acetate with mechanical agitation, 1.2 grams diphenylamine added, and 84.6 grams of tributyl acetylcitrate then stirred in. This solution was then added slowly in a fine stream to a vigorously agitated suspension of 189 grams of the RDX used in Example I and 2.4 grams lampblack chrome yellow pigment suspended in 3780 ml. of distilled water held at 80 C. When all of the nitrocellulose solution had been added, the temperature of the vigorously agitated mixture was raised gradually to 98 C. to drive off solvent. The suspension was then cooled quickly to 40 C. by passing water at about 16 C. through the jacket of the vessel used, and the whole vacuumfiltered. The granular product consisting of somewhat rounded particles having a maximum dimension range of about inch to inch, was placed inshallow trays and air-dried overnight. It was then oven-dried at 60 C. to constant weight.

The granular product thus prepared was further processed conventionally by rolling into sheets as described in Example I except that rolling at the smaller roll gap setting was only of such duration in order to obtain a product of uniform appearance, there being no solvent to evaporate. This material was also formed into billets by compression-molding. The processed flexible explosive prepared according to this example was substantially identical in properties with that of Example II with the exception that its Vacuum Stability Test value at 110 C. was 2.24 ml.

In addition to the use of rolling and compression molding for producing the desired shapes, we have found that the flexible explosive of this invention may be processed into sheets, blocks, and other forms by extrusion at temperatures preferably not in excess of F. Even long filaments of only inch diameter have been prepared by this method.

Blocks of the flexible explosive of this invention have been found to withstand relatively high impact without breakage, undue distortion, or excessive bounce.

While the present invention has been described in detail, it will be apparent to those skilled in the art that there are many variations possible without departing from the scope of this invention which is limited only by the appended claims.

We claim:

1. A self-supporting, resilient, high-powered, brisant, flexible exposive composition of moderate cap-sensitivity, low impact sensitivity, good heat stability and water resistance comprising about 45-76 weight percent of a high explosive selected from the group consisting of cyclotrimethylenetrinitramine (RDX) and cyclotetramethylenetetranitramine (HMX), about 17-39 weight percent of a plasticizer having a pour point not exceeding about -40 C., and about 5-15 weight percent of a high viscosity nitrocellulose containing about 12.1-12.5 weight percent nitrogen.

2. The composition of claim 1 further characterized by said RDX and HMX having an average particle size of up to about 25 microns and preferably not exceeding about 13 microns.

3. The composition of claim 1 wherein said plasticizer is selected from the group consisting of tributyl acetylcitrate, dioctyl sebacate and triethylene glycol di(2-ethylbutyrate).

4. An explosive composition in accordance with claim 1 wherein 100 parts thereof contain an additional 0.4 part of diphenylamine as stabilizer.

5. An explosive composition in accordance with claim 1 wherein said flexible explosive contains about 0.2 to 1.0 weight percent of a pigment consisting essentially of one part lampblack and 8 parts chrome yellow, medium.

6. A method for the preparation of a granular, highpowered explosive composition of moderate cap-sensitivity, low impact-sensitivity, good heat stability and Water resistance comprising the steps of dissolving about 8 parts high viscosity nitrocellulose containing about 12.1 to 12.5% nitrogen in about 240560 parts of butyl acetate,

dissolving about 0.4 part diphenylamine stabilizer in said solution,

adding about 2530 parts of tributyl acetylcitrate plasticizer to the stabilized solution,

suspending about 0.2 to 1.0 parts of a pigment consisting essentially of one part lampblack and 8 parts chrome yellow, medium and about 63 parts of a high explosive selected from the group consisting of HMX, RDX, and a mixture of HMX and RDX in water at 80 C. weighing about 58 to 60 times the Weight of said high explosive to form a suspension, slowly adding said stabilized nitrocellulose-diphenylamine solution to said rapidly stirred suspension maintained at 80 C. until addition of said stabilized solution is complete,

continuing the stirring while raising the temperature of said mixture to about 98 C. to drive off the solvent,

cooling said heated mixture rapidly to about 40 C.,

filtering said cooled mixture and drying the solid product to obtain said granular explosive.

7. The method of claim 6 wherein said butyl acetate comprises 384-400 parts.

8. A method for the preparation of a self-supporting, resilient, high-powered, brisant, flexible explosive sheet composition of moderate capensitivity, low impact-sensitivity, good heat stability and water resistance comprising the steps of mixing about 31.5 parts of a high explosive comprising dry RDX containing about 7.3 dry HMX and about 14.1 parts tributyl acetylcitrate plasticizer at about 135 F. to form a pasty mass,

mixing thereinto about 4 parts of a high viscosity nitrocellulose containing about 12.1 to 12.5% nitrogen and 0.4 part of a pigment consisting of 1 part lampblack and 8 parts chrome yellow, medium. to form a mixture,

adding ethanol to said mixture to form a thick dough,

mixing said dough at a temperature in the neighborhood of about 135 F. and

roll milling said mixed dough at about 135 F. to form said flexible sheet explosive composition.

9. A method for the preparation of a self-supporting, resilient, high-powered, brisant, flexible explosive sheet composition of moderate cap-sensitivity, low impact sensitivity, good heat stability and water resistance comprising the steps of mixing at F. about 12.60 pounds (dry basis) of a high explosive, RDX containing about 7.3% HMX and about 30% water, with 5.64 pounds of tributyl acetylcitrate plasticizer to form a first mixture, decanting the water from said first mixture,

adding to said recanted first mixture 1.60 pounds of a high viscosity nitrocelluolse, calculated on a dry basis and containing about 12.1 to 12.5% nitrogen, said nitrocellulose containing about 50% ethanol, and about 0.16 pound of a pigment consisting of 1 part lampblack and 8 parts chrome yellow, medium to form a second mixture,

mixing said second mixture for about 30 minutes at about 130 F., and roll milling said second mixture at about F. to form said flexible sheet explosive composition.

10. The process as described in claim 9 wherein the high explosive used is HMX containing about 12% RDX.

11. The process as described in claim 9 wherein said high explosive used in RDX containing about 2.5% HMX.

12. The process of claim 9 further characterized by adding 0.4 part of diphenylamine stabilizer dissolved in the ethanol contained in said nitrocellulose.

13. A method for the preparation of a granular, highpowered explosive composition of moderate cap-sensitivity, low impact-sensitivity, and good heat stability and water resistance comprising the steps of dissolving about 24 grams of a high viscosity nitrocellulose containing about 12.1 to 12.5% nitrogen in about 1176 grams butyl acetate solvent to form a solution, adding about 1.2 grams diphenylamine and 84.6 grams of tributyl acetylcitrate plasticizer to said solution.

slowly adding the resultant solution into an agitated suspension of '189 grams of a high explosive selected from the group consisting of RDX, HMX, and a mixture of RDX and HMX, 2.4 grams of a pigment consisting of 1 part lampblock and 8 parts chrome yellow, medium in about 3780 ml. of distilled water maintained at 80 C. to form a mixture.

raising the temperature of said mixture to about 98 C., cooling said heated mixture rapidly to about 40 C. and filtering said cooled mixture to separate said granular explosive.

References Cited by the Examiner UNITED STATES PATENTS 3,138,501 6/1964 Wright 149-92 3,235,420 2/1966 Murphy 14918 BENJAMIN R PADGETT, Primary Examiner.

| l l l i 

1. A SELF-SUPPORTING, RESILIENT, HIGH-POWDERED, BRISANT, FLEXIBLE EXPOSIVE COMPOSITION OF MODERATE CAP-SENSITIVITY, LOW IMPACT SENSITIVITY, GOOD HEAT STABILITY AND WATER RESISTANCE COMPRISING ABOUT 45-76 WEIGHT PERCENT OF A HIGH EXPLOSIVE SELECTED FROM THE GROUP CONSISTING OF CYCLOTRIMETHYLENETRINITRAMINE (RDX) AND CYCLOTETRAMETHYLENETETRANITRAMINE (HMX), ABOUT 17-39 WEIGHT PERCENT OF A PLASTICIZER HAVING A POUR POINT NOT EXCEEDING ABOUT -40* C., AND ABOUT 5-15 WEIGHT PERCENT OF A HIGH VISCOSITY NITROCELLULOSE CONTAINING ABOUT 12.1-12.5 WEIGHT PERCENT NITROGEN.
 2. THE COMPOSITION OF CLAIM 1 FURTHER CHARACTERIZED BY SAID RDX AND HMX HAVING AN AVERAGE PARTICLE SIZE OF UP TO ABOUT 2K MICRONS AND PREFERABLY NOT EXCEEDING ABOUT 13 MICRONS. 